FR2630253A1 - METHOD FOR IMPROVING THE FIRE RESISTANCE OF A DRY ELECTRICAL TRANSFORMER - Google Patents

Abstract

Process for improving the fire resistance of a winding of a dry electrical transformer impregnated with resin, characterized in that said winding is surrounded on its inner and outer faces, with a material based on fiberglass which has been pre-impregnated with a resin, of the same type as the impregnation resin and heavily loaded with incombustible products.

Description

Method for improving the fire resistance of a transformer winding

  The present invention relates to a method for improving the fire resistance of a dry electrical transformer winding. In particular, the invention applies to high voltage winding of a

Electric transformer.

  We know a process in which there is glass fabric in the body of the winding, for example between the different wafers, in the case of a wafer in wafers, or between the layers of conductors.

  in the case of a winding produced in long layers.

  In this process, the winding is also surrounded on its internal and external faces with a glass fabric. The assembly is then placed in a mold in which a vacuum is produced, then injected into it

  a generally flame retardant polymerizable resin.

  This process gives the coil good resistance to thermal shock. Indeed, the whole glass fabric and resin presents a

  coefficient of expansion close to that of electrical conductors.

  In addition, this process also gives, thanks to the resistance of the tissues

  glass, very good resistance to electrodynamic stresses.

  However, such a winding, even coated with a flame-retardant resin, does not make it possible to meet certain very demanding tests

fire resistance.

  Another method is known in which the high-voltage winding is coated in a resin heavily loaded with silica, of the order of

  65%, which improves the fire resistance of the transformer.

  However, in such a case, little or no glass fabric is used in or around the winding, since these fabrics act as a filter during the injection of the charged resin making it difficult to pour the resin. The absence or the small quantity of glass fabrics impregnated with resin greatly reduces the resistance of the winding and its resistance to electrodynamic stresses. Furthermore, the resistance to thermal shock is also less good, because the coefficient of expansion of the resin and silica assembly is more different from that of

  electrical conductors, as in the previous process.

  The object of the present invention is to propose a method for improving the resistance to fire of an electrical transformer winding. The invention therefore relates to a method of improving the fire resistance of a dry electrical transformer coil impregnated with resin, characterized in that said coil is surrounded on its internal and external faces, with a material to glass fiber base which has been pre-impregnated with a resin of the same type as the resin

  impregnation and heavily loaded with non-combustible products.

  The non-combustible products used as resin filler are

  for example mineral flame retardants.

  Thus, this material, the fibers of which are covered with a resin sheath very loaded with non-combustible products, constitutes a shield

  thermal considerably improving the fire resistance of the winding.

  According to a first embodiment of the method of the invention, said impregnation resin is an unfilled resin, injected after the installation of said glass fiber-based material previously prepreg of said resin heavily loaded with non-combustible products. According to a second embodiment of the process of the invention, said impregnating resin is a resin loaded with silica, injected and polymerized before the installation of said material based on glass fiber previously prepreg of said resin heavily loaded with

non-combustible products.

  In this second embodiment, the winding is carried out without glass fabric; on the other hand, after the installation of the fiberglass-based material, around the internal and external faces of the winding, the winding receives a flame retardant polymerizable resin. In the first embodiment, the winding can advantageously be furnished with

  fiberglass-based and uncharged material.

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Claims (4)

  1 / A method of improving the fire resistance of a dry electrical transformer coil impregnated with resin, characterized in that said coil is surrounded on its internal and external faces, with a material based on fiberglass which has been pre-impregnated with a resin, of the same type as the impregnation resin, and   heavily loaded with non-combustible products.   2 / A method of improving the fire resistance of a dry electrical transformer winding, according to claim 1, characterized in that said products are flame retardant mineral products.   3 / Method according to one of claims 1 or 2, characterized in that   the resin used is a flame retardant epoxy resin.   4 / Method according to one of claims 1 to 3, characterized in that   said impregnation resin is an unfilled resin, injected after the placement of said fiberglass material beforehand   prepreg of said resin heavily loaded with incombus products- tibles.   / Method according to one of claims 1 to 3, characterized in that   said impregnation resin is a resin loaded with silica, injected and polymerized before the installation of said material based on glass fiber previously impregnated with said resin heavily loaded with non-combustible products. -